Centrifugally cast pole and method

ABSTRACT

Herein disclosed is a centrifugally cast pole having a substantially uniform wall thickness along the long axis of the pole. During centrifugal casting, molten metal is poured inside a rotating, tapered mold. As chilled liquid is poured over the outside of the rotating mold, the metal forms, or paints, to the contour of the mold interior creating a metal pole. By precisely controlling casting gyrations such as the spin, travel, pitch, and yaw of the rotating mold and the calibration and physical mechanisms of the casting machine, hollow, tapered, tubular metal poles are produced with previously unknown uniformity of wall thickness. The controlling principles, designs, and mechanisms of this centrifugal casting method enable wall uniformity to extremely high tolerances. By extension, the ability to precisely control the metal volume painted inside the mold allows, as a design choice, wall thickness variation in any embodiment if so desired.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to hollow structural members and morespecifically to hollow utility poles having tapered external dimensionsand substantially uniform wall thickness.

2. Description of the Prior Art

The geometric shape of tapered poles in high stress, high lateral-forceenvironments typically encountered in the utility industry inherentlyprovides the greatest cross-sectional strength at or near the base ofthe pole where reactive forces tend to combine and converge.

Problems associated with the use of wooden poles within the utilityindustry are numerous and well documented. These problems include groundline decay, the tendency of wooden poles to bend or arc under highlateral forces (thereby requiring the use of guying cables, anchors andother auxiliary hardware), deterioration caused by birds and otheranimals, vibration damage to attached hardware and fixtures, shortagesof suitable trees for producing large poles, and high breakage rate dueto natural and manmade forces. Additionally, wooden poles as a generalrule must be replaced after approximately 20-30 years of service. Ofparticular note, replacement and disposal of wooden poles is a mounting,exorbitant liability for companies, especially when these poles cannotbe incinerated due to regulatory mandates. Further, some utilitycompanies have resorted to wrapping their wooden poles in wire mesh toprevent damage to the poles by birds and other animals.

Other companies have resorted to using hollow concrete poles,particularly with regard to high voltage electric transmission systems,in order to overcome some of the difficulties associated with woodenpoles. Concrete utility poles, however, are expensive to produce, arevery heavy and require special heavy-duty equipment to load, transport,unload and install. Further, due to strength requirements, concretepoles are usually solid at the top, where the pole has its smallestdiameter. Moreover, field modifications of concrete poles are generallyvery time consuming, cumbersome and thus very costly.

Steel utility poles are currently available in the market. Steel polesare typically produced by cutting thin and malleable steel plates andforming the plates, using metal brakes and other hot and/or cold metalshaping methods, into two multi-sided halves which are then weldedtogether. Such poles are quite expensive to produce and, as aconsequence of the thin walls necessary to form them, result in poleshaving relatively large base diameters in order to achieve the necessarystrength to be used in high stress, high lateral-force situations suchas those subject to utility poles. Further, wall thickness can be variedonly sectionally, if at all.

Aluminum alloy utility poles are also available. However, these polesare generally appropriate for low stress, single-use application, suchas highway lighting. Further, aluminum poles are not currently formed bycentrifugal casting methods and are typically produced by hot or coldmetal-shaping methods. Moreover, aluminum poles do not have thenecessary qualities or strength to be used in high lateral-forceenvironments, such as those to which utility poles are subjected.

Ductile iron has characteristics which are ideal for use in the utilitypole environment. For example, ductile iron has a superiorstrength/weight ratio, is machineable, resilient (as opposed tobrittle), has favorable damping properties, is rust proof and is cheaperthan aluminum and concrete. Therefore, if centrifugally cast intogeometric shapes necessary for utility pole applications, ductile ironwould provide a virtually maintenance free, extremely long life (many100+ year old ductile iron water mains are still in use), low costutility pole which effectively overcomes the problems and difficultiesassociated with other utility poles as discussed hereinabove.

Centrifugal casting offers additional benefits over alternativeproduction techniques such as metal forming. For instance, centrifugalcasting produces a seamless pole, which ensures overall strength in highstress, high lateral-force environments. Furthermore, centrifugalcasting allows a large volume of poles to be produced inexpensivelythrough a mechanized process involving little human labor. Since long,seamless sections can be cast in a single pass, subsequent joiningprocedures during manufacture or field installation are reduced oreliminated. Also, centrifugal casting produces a much more precise polethan that created through metal forming, and is capable of producingpoles within tolerances of 0.001 mm. In summary, centrifugal castingproduces stronger, less labor-intensive poles that are more easily massproduced for a wider variety of applications.

Prior to the present invention, centrifugal casting of tapered metalutility poles (including ductile iron) has been limited by the castingtechnology. Single-speed casting methods (such as that disclosed inApplicant's prior U.S. Pat. No. 5,784,851) prevented the metal infusionfrom dispersing properly such that the amount painted on the inside ofthe mold as it spins and travels can be deposited end-to-end uniformlyto high tolerances (0.001 mm.). This has meant that centrifugal castingof tapered poles was only slightly more versatile than metal rolling,though there are other advantages mentioned hereinabove. The presentinvention overcomes this limitation by introducing a variable-speed,variable-infusion casting method, whereby the metal-painting isprecisely controlled by increasing or decreasing the metal pouring rateand the spin speed of the mold. Depending upon the desiredspecifications, poles can be formed with walls that are thick at bottomand thin at top, that vary in thickness at specified points, or that aresubstantially uniform in wall thickness along the long axis of the pole.

Further, the present invention allows production of poles that fulfillspecific application requirements. For example, while some applicationsrequire variable thicknesses (thin at the top, thick at the ground lineto resist line loads and corrosion), other applications may requireuniform thickness for maximized structural support. The presentinvention also fulfills applications that require extreme or variableheights, in that the poles may be cast with slip-jointed pole sections,whereby the tapered section of one pole can be secured into the butt endof another pole to reach specified effective pole lengths. Additionally,special applications may require further enhancement of the pole duringor post-casting including, but not limited to, wind-resistant texturing,mount flanges, hardware and fixture access holes or panels, and top-endcaps.

SUMMARY OF THE INVENTION

In view of the foregoing, the present invention relates to acentrifugally cast hollow pole having a wall thickness which issubstantially uniform along the long axis of the pole.

In one embodiment, a conically tubular pole having tapered externaldimensions and a substantially uniform wall thickness along the longaxis of the pole is produced via centrifugal casting, whereby moltenmetal is poured inside a rotating, tapered mold. As chilled liquid ispoured over the outside of the rotating mold, the metal forms, orpaints, to the contour of the mold interior creating a metal pole. Byprecisely controlling casting gyrations such as the spin, travel, pitch,and yaw of the rotating mold and the calibration and physical mechanismsof the casting machine, hollow, tapered, tubular metal poles areproduced with previously unknown uniformity of wall thickness. Thecontrolling principles, designs, and mechanisms of this centrifugalcasting method enable wall uniformity to extremely high tolerances. Byextension, the ability to precisely control the metal volume paintedinside the mold allows, as a design choice, wall thickness variation inany embodiment if so desired.

It is an object of the present invention to provide a hollow, taperedpole which is easy and economical to produce having a wall thicknessthat is substantially uniform along the length of the pole. The abilityof this new method to produce uniform wall thicknesses is especiallyimportant in applications where lateral forces can cause disastrousutility pole failure, such as by hurricane-force winds.

Another important advantage of the present invention is the centrifugalcasting of poles utilizing any molten materials such as ductile iron,steel, aluminum, or castable composite material, thereby rendering thepole virtually maintenance free and impervious to ground line decay,fungus, humidity, animal damage and other causes of deterioration.

A further advantage of the present invention is that a polecentrifugally cast of ductile iron would be comparatively lightweight,would have the physical strength of mild steel with the long lifeexpectancy of gray cast iron, would be virtually unbreakable in ordinaryservice and would be 100% salvageable.

Yet another advantage of the present invention is that a polecentrifugally cast of ductile iron would offer the greatest possiblemargin of safety against service failure due to ground movement and beamstresses and would provide increased resistance to breakage caused byhandling, shipping and installation.

An important advantage of the present invention is that molds can beproduced by welding, flanging or threading shorter sections togetherinto a single molding tube.

The invention is particularly advantageous in that a pole centrifugallycast can be direct buried or may be flanged for attachment to poured orpreformed foundations.

A further advantage of the present invention is that the hollow designof a centrifugally cast pole allows for internal wiring of fixtures andother attachments to said pole.

An important improvement to the present invention is the provision of atexturing process during casting that augments the strength of the pole.A mold with a textured interior wall surface may be utilized, therebyproducing a final product with a pimpled exterior surface. The resultingpimpled pole benefits through improved wind resistance in whateverembodiment and field of use.

To enhance extreme height/extreme stress applications, the pole may alsobe cast in such a way that the wall thickness near the butt of the poleis sufficient to accommodate the formation, during the castingoperation, of a slip joint having internal cross-sectional dimensionssufficient to allow the pole to slidably receive the top portion ofanother centrifugally cast pole whereby providing for virtuallyunlimited pole extensions.

Additionally, an end cap can be designed for field installation toprotect all internal hardware.

The present invention also addresses the post-cast annealing process ina new way. This new method begins during casting, whereby mold-inducedflanging of the large-diameter end of the tapered pole becomes, ineffect, a control-point for bearing the pole through the annealingprocess. The flange is simply a larger based circle, or ring, cast atthe pole's large-diameter end. Once the pole is removed from the mold,this flanged ring is engaged by a control rail such that the pole can berun through a straight annealing furnace. As the rail engages therunning ring, the tapered pole is prevented from inadvertently slidingor rolling from the conveyance as the pusher chains engage and move thepole through the furnace. This ring also allows the pole to be placedinside of a straight pipe which rolls through the annealing furnace.

Lastly, it is noteworthy that the present invention is not limited touse in the utility pole field. Rather, the present invention may beadvantageous wherever a structural pole member is needed. For instance,the present invention could be used as a tapered support piling. Thetapered shape of the piling would impart the necessary load capacitywhile minimizing the piling's embedment in the bearing stratum. Thetapered shape would also require less concrete volume to fill than atraditional cylindrical piling. Further, the piling could be pimpled onits surface to enhance the load bearing capacity of the piling. Finally,ductile iron would be an ideal choice for pilings because of itscompressive strength and corrosion resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of the presentinvention will be apparent from the following more particulardescription of preferred embodiments as illustrated in the accompanyingdrawings in which reference characters refer to the same partsthroughout the various views. The drawings are not necessarily to scale,emphasis instead being placed upon illustrating the principles of theinvention.

FIG. 1 is a side view of an embodiment of the invention showing theinvention in a direct burial configuration.

FIG. 2 is a side view of the embodiment of FIG. 1 showing the inventionin a flanged, based or foundation-mounted configuration.

FIG. 3 is a side view of the invention, partially sectioned, showing theslip joint design of the invention used for extended height.

FIG. 4 is a diagrammatic view of a typical centrifugal casting machinebeing used to cast an embodiment of the invention. Also shown, inpartial longitudinal section is the tapered mold.

FIG. 5 illustrates the use of the running ring and the third rail beingused to control the tapered pole as it rolls through an annealingfurnace.

FIG. 6 shows the effective use of a dimpled surface to createturbulence, thereby reducing wind loading on the pole during high windconditions.

FIG. 7 shows the procedure required to produce a long tapered mold,which is machined inside.

DETAILED DESCRIPTION OF THE PREFERRED INVENTION

FIG. 1 shows a hollow, centrifugally cast, utility pole 1 in a directburial configuration according to an embodiment of the invention. FIG. 2shows the invention in a pedestal or foundation-mounted configurationaccording to a second embodiment of the invention. The pole 1 of FIGS. 1and 2 has been centrifugally cast in a manner which imparts a taperedshape to the external linear dimensions of the pole 1 from pole butt 2to pole top 3 as shown. The tapered shape of the pole 1 gives the pole 1added strength and also saves raw materials during the castingoperation. The embodiments of FIGS. 1 and 2 further comprise a pole cap4 and pre-drilled or field modified holes 5 for attachment of typicalutility pole hardware and fixtures. Also shown in the embodiment of FIG.1 is an access panel 6. Said panel 6 is located near the bottom interioror core 7 of the pole 1 in situations where internal hardware such ascables or wires have been installed within said hollow core 7. Thecentrifugal casting of the tapered pole 1 provides for the controlledwall thickness 8 along the entire length of the pole 1 whereby the wallthickness imparted to the pole 1 is controlled by design from pole top 3to pole butt 2. This controlled wall thickness 8 provides greater designflexibility and strength to the pole 1.

FIG. 2 shows the pole 1 with a flange 9 at its butt 2 to enable the pole1 to be mounted and secured to a foundation 10 or other pedestal-typeapparatus. In this embodiment, the pole 1 is shown secured to thefoundation 10 by a plurality of bolts 11 and nuts 12.

FIG. 3 shows the press-fit, slip joint 13 configuration of the inventionused to interconnect two or more cast pole 1 sections for extendedheight. The slip-joint 13 comprises a tapered, centrifugally cast,utility pole 1, according to the invention, wherein the internal core 7diameter of the pole 1, beginning at the butt 2 of the pole 1 andextending internally linearly along a portion of the length of the pole1, has been cast to have internal dimensions which allow the butt 2 ofthe pole 1 to slidably engage the top portion 3A of anothercentrifugally cast tapered pole 1A. Such interconnection provides forvirtually unlimited extensions of pole 1 height.

FIG. 4 shows a typical centrifugal casting machine 14 being used to castan embodiment of the invention. An internally tapered mold 15 is similarto conventional centrifugal casting molds with the exception of theinternal linear dimensions of the mold 15 as shown in the longitudinalcross-section of the mold 15 is generally circular in form, however, theinternal surface of the mold 15 could be modified to produce taperedpoles having multisided dimensions such as poles with generally squareor polygonal cross-sections. In the preferred embodiment of pole 1, aninternally tapered chill-type mold 15, is used to impart a taperedexternal shape to the pole 1. Depending on the particular applicationand strength required of the pole 1, the overall wall thickness 8 (FIGS.1 and 2) of the pole 1 may be varied during the casting operation by thepouring rate of material 16 allowed to enter the centrifugal castingmold 15 and by varying the RPM of the motor 17 also by the travel speedof the machine 18.

Also shown in FIG. 4 is a core mold 19 used to faun the slip-joint 13(FIG. 3) of the invention during the centrifugal casting process. Whendesired, said core mold 19 is inserted into the mold 15 at the butt 2(FIGS. 1 and 2) of the pole 1 being centrifugally cast. When presentduring the centrifugal casting operation, the core mold 19 causes thecore 7 (FIGS. 1 and 2) diameter of the cast pole 1 to be uniformlycontrolled along the length of said core mold 19. The core 7 (FIGS. 1and 2) diameter formed by the use of said core mold 19 during thecentrifugal casting process is sufficient to enable the butt 2 (FIGS. 1and 2) of the pole 1 after casting to slidably engage the top portion 3A(FIG. 3) of another centrifugally cast pole 1A (FIG. 3).

FIG. 5 shows tapered pole 1 as it is pushed through the annealingfurnace by pusher chains 20 and 21 along running rails 22, 23 and 24. Astapered pole 1 begins to travels in a circular path along running rails22, 23 and 24, running ring 25 engages the third running rail 24,thereby allowing the tapered pole 1 to run essentially straight throughan annealing furnace. The running ring 25 also allows for tapered pole 1to be inserted into a conventional round pipe and carried thru anannealing furnace.

FIG. 6 shows texture (pimples) 26, which are cast into the surface ofthe pole's exterior during the manufacturing process. These pimples 26are effective in reducing wind resistance on the face of the pole.

FIG. 7 illustrates one method of producing a tapered mold 15. Thetapered mold 15 is made by matching various short tapered tubes 27, 28,29, and 30 that have been machined prior to being welded into one longsection, eliminating the need to bore long tapered I.D. holes.

While the invention has been particularly shown and described withreference to the preferred embodiments thereof, it will be understood bythose skilled in the art that various alterations in form, detail andconstruction may be made therein without departing from the spirit andscope of the invention.

1-24. (canceled)
 25. A hollow, tapered, cylindrical structural memberhaving an outer diameter that varies along a length of the member,comprising: a tapered, cylindrical wall made of a metallic material,wherein a first portion of the tapered cylindrical wall has a firstthickness, wherein a second portion of the tapered cylindrical wall hasa second thickness that is different from the first thickness, whereinthe thickness of the tapered cylindrical wall is substantially constantalong a majority of the length of the structural member, and wherein aninterior surface of a large diameter end of the tapered cylindrical wallhas a shape and dimensions that would allow an external surface of asmall diameter end of a second hollow, tapered, cylindrical structuralmember to be inserted into the large diameter end of the taperedcylindrical wall; and a flange that extends radially outward from anexterior side of the large diameter end of the tapered cylindrical wall.26. The hollow, tapered cylindrical structural member of claim 25,wherein an interior diameter of the structural member narrows along thelength of the cylindrical wall.
 27. The hollow, tapered cylindricalstructural member of claim 25, wherein the thickness of the firstportion of the tapered, cylindrical wall is substantially uniform alongthe length of the first portion, and wherein the thickness of the secondportion of the tapered, cylindrical wall is substantially uniform alongthe length of the first portion.
 28. The hollow, tapered cylindricalstructural member of claim 25, further comprising an access aperturethat extends through the tapered, cylindrical wall adjacent the largediameter end of the tapered, cylindrical wall.
 29. The hollow, taperedcylindrical structural member of claim 25, wherein the access apertureis generally rectangular in shape.